Dead Kokanee discovered in Lake Koocanusa

Higher water temperatures and areas of the lake with dissolved oxygen are likely causes, according to a fisheries biologist.

Dead Kokanee salmon discovered in Lake Koocanusa part of a recent phenomenon likely caused by low water temperatures and dissolved oxygen.

Dead Kokanee salmon discovered in Lake Koocanusa part of a recent phenomenon likely caused by low water temperatures and dissolved oxygen.

A fisheries biologist says there’s no reason for alarm after some dead Kokanee salmon were recently discovered by anglers out on Lake Koocanusa.

Reported by a local marina out on the lake, Heather Lamson, a local fisheries biologist with the Ministry of Environment, took samples on Tuesday and shipped them off to a lab in Duncan.

Results should be back in a few weeks, but Lamson already suspects that the cause is likely due to a phenomenon that is becoming more and more common.

“It is an annual event, it seems to be in the last few years we’ve had a die-off of Kokanee on Koocanusa, at least for the last three years,” Lamson said.

“It’s always in August, so it’s always a pretty typical summer kill probably, most likely related to high temperatures and low dissolved oxygen.

“Because Kokanee are a schooling fish, they’ll school up and they’ll all sort of swim into potentially dangerous water for them, the water that is separated and often you’ll find in lakes where it’s not very windy for a few days, you’ll find a separation of water layers and certain water layers have depleted oxygen so if fish end up in those layers, they can die.”

Though that is the most likely cause, she isn’t necessarily ruling out blue-green algae or other bacterial or viral causes, which is what the lab tests will determine.

Higher water temperatures and bodies of water with dissolved oxygen isn’t anything unique to Lake Koocanusa.

She noted that the water temperature was roughly 20 degrees Celsius when she went out to the lake on Tuesday. As of Thursday morning, the water level at the lake is at 2,441 feet.

“It does happen throughout North America too, it’s not just Koocanusa that this happens at—it happens on Kootenay Lake, where Kokanee are native; they’re not actually native in the Kootenay watershed,” said Lamson.

“The Island has had reports, Okanagan Lake has had reports. It is fairly common and fisheries biologists link it to high temperatures and low dissolved oxygen.”

She notes that she only saw four dead salmon even though there were reports of roughly 100 between Newgate and the mouth of the Elk River, adding that these events affect a fraction of the Kokanee population.

“Because they’re such an abundant species, on a population scale, it doesn’t have that much of an effect, we’re not seeing the whole Kokanee stock being diminished because of these kills,” Lamson said.


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